Find a chronograph you can use to get the exact muzzle velocity. Then you can put your BC ,weight of the bullet, velocity, zero yardage and alltitude in one of the many online ballistic calculators. You can deduct 25fps for every inch of barrel you are short for a ballpark it should come out close. The only way to know for sure is to chronograph it some barrels are faster or slower then others.
Good luck.